Pneumatic starter overtemperature control

ABSTRACT

An aircraft engine starter including a pneumatic motor driven by pressurized gas upon opening of an upstream control valve. A fusible plug valve automatically closes the control valve and shuts down the pneumatic motor whenever temperature of the lubricating oil of the motor exceeds a preselected level.

This is a division of application Ser. No. 886,381 filed Mar. 13, 1978,now U.S. Pat. No. 4,220,439.

BACKGROUND OF THE INVENTION

This invention relates to pneumatic control systems and relates moreparticularly to pneumatic starters for use in starting aircraft engines.

Typically a pneumatic starter of the class referred to includes a fixedlevel oil sump and normally operates for a short duty cycle whilestarting the engine of an aircraft. In the instance of systemmalfunction the starter many times operates undetected after enginestarting and is subject to overspeeding and overheating. This typicallyresults in severe internal damage to the starter and often times causessecondary damage to associated components.

A continuing problem for such a system has been in detecting the systemmalfunction which can ultimately cause starter overspeeding anddestruction. Problems of detection of this event are compounded by therelatively short duty cycle of the starter, its small torque drag on alarge aircraft engine, and relatively inconsequential effect on engineperformance prior to damage to secondary components. Usually theoccurrence of such a malfunction is first noted after severe damage tothe starter.

Accordingly it will be apparent that there exists a need for a mechanismand method for sensing malfunction in a timely fashion to permitpreventive measures to be taken prior to starter destruction. Whileprior art systems such as illustrated in U.S. Pat. Nos. 1,248,143;1,600,322; 1,712,116; 1,783,395; 2,707,864; 2,741,085; 3,008,688;3,338,255; and 3,817,353, have certain similarities with the presentinvention, none of these prior art systems recognize the discoveriesassociated with the present invention nor the attendant results inspecific structure and method thereof.

SUMMARY OF THE INVENTION

Accordingly it is a broad objective of the present invention to providean improved control system and method which can detect a malfunction ina pneumatic starter and take preventive action to avoid destruction orsevere damage to the starter as a result of this malfunction.

More particularly, it has been discovered that the temperature oflubricating oil of such a pneumatic motor for starting an aircraftengine can be utilized to determine a malfunction of the classdescribed. Further, in accord with this discovery the present inventioncontemplates an improved system and method wherein the temperature ofthe lubricating oil of the motor is sensed, and a pneumatic valve isactuated whenever this temperature exceeds a preselected value in orderto shutdown motor operation and prevent continued operation thereof tothereby avoid the serious damage to the motor and associated components.

In summary the present invention contemplates a fusible plug valve whichhas a valve section that normally blocks fluid communication from anactuator to an exhaust port. Development of high pressure in theactuator is operable to open an inlet control valve to permit motive gasflow to the motor to operate the same. The shutoff valve is held in itsclosed position by a fusible metal joint, such as solder, which isexposed to the lubricating fluid of the motor and melts whenevertemperature thereof exceeds a preselected value. In response, theshutoff valve opens communication from the actuator to an exhaust portto relieve pressure in the actuator and cause the inlet control valve toclose. This discontinues motor operation and prevents restartingthereof. The shutoff valve is also configured such that a visibleindicator is present when the fusible material has melted.

A concomitant object of the present invention is to provide a simple,economical, improved fuse plug valve structure of the class described.

These and other objects and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the preferred embodiment of the invention whenread in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view of an aircraft engine starter ascontemplated by the present invention with portions broken away toreveal details of construction;

FIG. 2 is an exploded perspective view of the components of the fusiblevalve structure of the present invention;

FIG. 3 is a partially cross-sectional, partially schematic diagram of apneumatic control system utilizing the present invention;

FIG. 4 is an elevational cross-sectional view of the fuse plug valve anda portion of the lubricating oil sump;

FIG. 5 is a view similar to FIG. 4 but showing the shutoff valve in itsopen position; and

FIG. 6 is a plan cross-sectional view taken along lines 6--6 of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to the drawings, an aircraft enginestarter denoted generally by the numeral 10 includes a pneumatic motorin the form of a radial inflow turbine 12 disposed within a casing 14which has an inlet port 16 and an exhaust port 18. Also within casing 14is a gear box or accessory component and overrunning clutch connected todrive an output shaft 20. In the general area of the transmission is afixed level oil sump containing lubricating fluid normally in the formof oil or other liquid 22. Associated with inlet port 16 is a source 24of motive, pressurized gas delivered to inlet port 16 across a controlvalve in the form of a butterfly valve 26. Control valve 26 is biased toits closed position illustrated in FIG. 3 by a spring 28 acting througha piston 32 and appropriate connecting linkage. Actuating means in theform of a cylinder 30 and cooperating piston 32 in operative associationwith control valve 26, are operable to shift the control valve to anopen position permitting motive gas flow to inlet port 16 by delivery ofa pressurized fluid to the lower end of piston 32 to cause upwardmovement of the piston.

Associated with the control valve actuator is a pneumatic control systemfor porting fluid to opposite sides of piston 32. This control systemincludes a conduit 34 receiving a flow of pressurized fluid or gas froman appropriate source, such as the same source 24, and communicates bothwith a pneumatic switcher valve 36 and a start valve 38. Switcher valve36 communicates with the portion of cylinder 30 above piston 32 and isoperable to deliver presssurized fluid from conduit 34 to the upper sideof piston 32 in the position illustrated. Energization of the piston 40of switcher valve 36 shifts ball 42 upwardly to close communication ofpressure, and allow exhaust of pressurized gas from the upper side ofpiston 32 through a bleed orifice 44. Start valve 38 includes a ballvalve 46 positionable in its upward position shown in FIG. 3 whereinpressurized fluid from the lower end of piston 32 is exhausted throughconduit or duct 48 to an exhaust 50. Valve 46 may be shifted downwardlyto port pressurized gas into conduit 48, through orifice 49 to the lowerside of piston 32 either by energization of solenoid 52 or by depressionof a manually operable plunger 54. It will be apparent that uponshifting valve 46 downwardly, the lower side of piston 32 is pressurizedand the control valve 26 is rotated to an open position permittingmotive gas flow to inlet port 16 to drive motor 12. Similarly, exhaustof pressurized gas from the lower side of piston 32 permits the helicalspring 28, and/or pressure on the upper side of piston 32 to drivecontrol valve 26 to its closed position to shut down and interruptoperation of turbine 12.

Associated with the sump portion of casing 14 and the conduit 48 of thecontrol system is a fuse plug valve means in the form of a heatsensitive pneumatic dump valve or fusible plug 56. Plug valve 56includes a body which may either be unitary or as illustrated comprisethree separate but intersecured components: a first elongated inner plug58, a second elongated outer plug 60, and a fitting 62 disposedintermediate and in surrounding relationship to plug 60. Plug 58 isthreadably secured to and extends through casing 14 with an inner endthereof immersed in the lubricating oil 22. The opposite ends of plug 58have inner and outer counterbores 64, 66 which are interconnected by asmaller diameter central opening 68. The inner end of plug 60 isthreadably secured within outer counterbore 66, and plug 60 also has anouter counterbore 70 whose outer end opens to the atmosphere andpresents an exhaust duct for relieving pressurized gas. A second centralopening 84 in plug 60 is in alignment with the central opening 68 ofplug 58. A first set of cross holes 72 at the inner end of plug 58 opensinto inner counterbore 64 to assure total immersion thereof in thelubricating liquid 22, while the outer counterbore 70 of plug 60 alsohas a second set of cross holes 74 that open into counterbore 70.Fitting 62 surrounds the mid portion of plug 60 and the cross holes 74with an inlet port 76 communicating with outer counterbore 70 throughcross holes 74. Inlet port 76 communicates with conduit 48 via an airline 78 downstream of orifice 49. Seals 82 are included to secure theplug 58, 60 and fitting 62 into a unitary, sealed, hollowed valvingbody.

Disposed within the interior of the valve body is a movable shutoffvalve in the form of an elongated stem valve 86. Valve 86 includes alower valve section in the form of a piston 88 normally disposed insealing relationship with outer counterbore 70 through an appropriateseal such as an O-ring 90. The opposite inner end 92 of valve 86 isdisposed within inner counterbore 64 and immersed in lubricating oil 22.A reduced diameter, elongated stem section 94 extends between andintersecures the piston 88 to the inner end 92 of the valve. Stem 94extends through the aligned central openings 68, 84 and an appropriateseal 96 cooperates with the plug 60 and stem section 94 to preventcommunication between the lubricating liquid 22 and the gas receivedthrough inlet port 76. Biasing or spring means in the form of a helicalcoil compression spring 98 is disposed within outer counterbore 70 andextends between piston 90 and a transverse shoulder 100 formed at thereduced diameter section of plug 60. Spring 98 urges piston 88 outwardlytoward the open position illustrated in FIG. 5 wherein the piston 88clears the exhaust port end of counterbore 70.

Against the bias of spring 98, the piston 88 is maintained in its FIG. 4closed position by fusible metal material, such as solder, defining anannular joint 102 which secures the inner end 92 of the valve to theinner end of plug 58. The fusible material of joint 102 is so selectedto melt whenever the temperature of lubricating oil 22 exceeds itsnormal operating temperature.

In operation, energization of solenoid 52 or depression of plunger 54shifts ball valve 46 downwardly to deliver pressurized fluid to thelower side of piston 32 and shift valve 26 toward an open position.Pressurized motive gas is then delivered to the inlet of turbine motor12 to initiate operation of the starter. It has been found that in theevent of a malfunction in the system which would otherwise cause seriousdamage to the starter motor, the temperature of the lubricating oil 22rises above its normal operating level. Fusible material 102 ispreselected so as to melt at a preselected temperature which is slightlyabove the normal operating temperature of the lubricating oil, such aswithin a range of 450° F. to 465° F., to allow the bias of spring 98 andthe pressure of fluid from inlet port 76 to shift piston 88 downwardlyto its FIG. 5 position completely clearing the exhaust port outer end ofcounterbore 70. This immediately relieves pressure from conduit 48 andthe lower side of piston 32 to permit the control valve 26 to shift toits closed position illustrated in FIG. 3. Pressure is relieved from thelower side of piston 32 even if pressurized fluid is still beingdirected into conduit 48 from source 24, due to the inclusion of theflow limiting orifice 49. The interruption of motive gas flow to turbine12 thus shuts down the air turbine starter before damage occurs. It willalso be apparent that the motor cannot be restarted with the piston 88in its FIG. 5 open position.

The fusible plug is configured with the valve 86 arranged relative tothe valve body so that the piston 88 shifts to a position exteriorly ofthe body to be readily visible upon melting of the fusible material.Accordingly, the present invention provides a readily visible indicationthat a malfunction has occurred while at the same time shutting downmotor operation to prevent damage thereto.

The overall configuration of valve 56, especially its three part bodyand cooperating dump valve 86 presents an extremely compact, economicalstructure which relieves pressure upon actuation, permits retrofittingto existing motor units in a straightforward manner due to theconfiguration of its temperature sensing structure while controllingoperation of a remotely located valve 26, and yet also provides avisible indicator when actuated.

From the foregoing it will be apparent that the present inventionpresents a method of providing automatic shutdown capabilities in anaircraft engine pneumatic starter in the event of malfunction, whichmethod includes steps of delivering a flow of pressurized fluid toturbine motor 12 to operate the turbine; delivering a pressurized fluidto operate the piston 32 of the actuator to open the control valve 26 topermit flow to the turbine motor; providing a dump valve 86 which in anormally closed position allows motor operation but which iscontinuously urged by spring 98 to an open position exhaustingpressurized gas from the piston to close the control valve 26; andsecuring dump valve in its normally closed position by the fusibleannular joint 102 which melts in response to overtemperature of thelubricating oil to allow the dump valve to move to its open position.

Various alterations and modifications to the specific structureillustrated and described will be apparent to those skilled in the art.Accordingly, the foregoing detailed description of a preferredembodiment of the invention should be considered exemplary in nature andnot as limiting to the scope and spirit of the invention as set forth inthe appended claims.

Having described the invention with sufficient clarity that thoseskilled in the art may make and use it, we claim:
 1. A method ofproviding automatic shutdown capabilities in an aircraft enginepneumatic starter in the event of a failure creating excessive heatwithin the starter, comprising the steps of:delivering a flow ofpressurized fluid to operate an actuator to open a control valve;directing a flow of pressurized gas across said opened control valve tosaid starter to operate the latter; providing a dump valve having aclosed position blocking communication between the actuator and anexhaust port to permit normal starter operation; continuously urging thedump valve toward an open position connecting the actuator with theexhaust port to close said control valve and thereby interrupt the flowof pressurized gas and shut down starter operation; and securing thedump valve in its closed position by a heat sensitive fusible materialimmersed in the lubricating oil of the starter, said fusible materialmelting whenever said lubricating oil exceeds a preselected temperatureto permit the dump valve to move to its open position and automaticallyshut down starter operation.